Mill scale is iron oxide formed on the surfaces of steel slabs, blooms, or the like during hot rolling operations in a steel mill. It is customary to effect mechanical removal of the mill scale by means of scale breakers or high pressure water sprays. The mill scale is collected in a scale pit as a thick slurry or sludge which may contain on the order of 10-15% water. In addition, the mill scale contains on the order of 1/2 to 1% oil as a contaminant resulting from the use of hydrocarbon oil as a lubricant in various portions of the rolling equipment. Mill scale has a high iron content, for example, on the order of 70%, and is therefore a valuable material if it can be utilized in a steelmaking operation.
Heretofore, it has been customary to utilize mill scale as a component of the sinter mix fed to a sintering line. However, it has been found that almost 100% of the oil contained in mill scale used for sintering is removed from the sinter bed in the form of a hydrocarbon oil vapor which is discharged into the atmosphere by the exhaust gases of the sintering process. Because of present day air pollution regulations which forbid the discharge of hydrocarbon vapors into the atmosphere, the steel industry is faced with the possibility of not being able to use large tonnages of oil-bearing mill scale in sintering operations. Furthermore, the use of oil-bearing mill scale in a sintering operation results in excessive coating and fouling of the fans in the gas circulation system so that periodic shutdowns are necessary in order to clean the fans.